A magnetoresistive random access memory (MRAM) is a nonvolatile magnetic memory capable of high-speed operation. Therefore, MRAMs are expected to serve as novel nonvolatile work memories, and are being developed by a large number of organizations. An MRAM includes a magnetic tunnel junction (MTJ) element as a storage element. The fundamental structure of an MTJ element is formed with three layers, which are a magnetic layer, an insulating layer, and another magnetic layer. One of the magnetic layers is called the storage layer, and the other one of the magnetic layers is called the reference layer. The intermediate insulating layer is called the tunnel barrier, and is formed with an insulating film that is very thin but can allow a tunneling current to flow.
In an MRAM including a MTJ element as a storage element, write and read operations are performed by applying current between the storage layer and the reference layer via the tunnel barrier. Therefore, the tunnel barrier might break at the time of writing, and read disturb might occur as the magnetization of the storage layer is switched at the time of data reading.
To counter this, SOT-MRAMs have been suggested. In an SOT-MRAM, the magnetization of the storage layer of an MTJ element is switched by a spin Hall effect or spin orbit torque (SOT), and thus, writing is performed. However, such an SOT-MRAM has the problem of an increased cell area, as will be described later.